The extrusion of generally flat, wide panels, e.g. of polyvinylchloride or other synthetic resin material or plastics, generally utilizes an extruder upstream of the die, a die body formed with a passage leading from the extruder, and a die lip which defines the extrusion orifice and which can be mounted on the die body by screws or the like.
In U.S. Pat. No. 4,015,925, for example, the die lip is a substantially rectangular parallelepiped in which the extrusion orifice is formed and in which, moreover, the die lip is constituted from two relatively large members drawn together transversely to the orifice by cap screws located at opposite ends of the die lip and flanking the orifice perpendicular to a parting plane between the two members.
The edges of the siding extrusion which is formed can have complex contours as defined, for example, by insert members anchored in respective recesses to either side of the parting plane by respective setscrews.
In this construction, the sealing of the two lip members together is dependent upon the tightness with which the cap screws can hold the two lip members against each other.
This system has the disadvantage that considerable torque must be applied to the cap screws and that any tendency of the cap screws to relax to even the slightest may interfere with an effective seal.
The assembly of the die lip was also unduly complicated in this arrangement.